From President Barack Obama, on enforcing federal drug laws in Colorado and Washington, where voters have made marijuana use legal:
We've got bigger fish to fry....It would not make sense for us to see a top priority as going after recreational users in states that have determined that it's legal.
For what it's worth, I don't think anyone should take this as meaningful. The federal government doesn't "go after" recreational users right now, and no one thinks they're going to start. But they do go after growers and distributors of pot, and Obama said nothing at all about that. This is basically a non-response and probably shouldn't be taken as an indication of what federal policy is likely to be going forward.